1. Field of the Invention
The present invention relates to a merged or a piggyback magnetoresistive (MR) head which has a sunken insulation stack region, wherein components such as inductive pole pieces, coil layer and insulation layers are contained.
2. Description of the Related Art
A merged or piggyback MR head includes a read head portion and a write head portion, the write head portion being located on top of the read head portion. The read head portion includes an MR sensor sandwiched between first and second gap layers which are, in turn, sandwiched between first and second shield layers. The MR sensor has an outside edge which is exposed at an air bearing surface (ABS) for reading data from a moving magnetic medium, such as a rotating magnetic disk. Changes in magnetized regions on the rotating magnetic disk induce corresponding resistance changes in the MR sensor which are detected in the form of potential changes when a sense current is conducted through the MR sensor. The write head portion includes a coil layer (write coil) sandwiched between insulation layers which are, in turn sandwiched between first and second pole pieces. The pole pieces terminate in pole tips and are magnetically connected at a back gap, the pole tips being separated by a thin gap layer at the ABS forming a transducing gap. The separation of the pole tips is referred to as the "write gap". Flux across the write gap is recorded as information on circular tracks in the rotating magnetic disk.
In a piggyback MR head the second shield layer and the first pole piece are separate layers; in a merged MR head the second shield layer and the first pole piece are merged in a common layer which functions as a write pole during a write operation and as a second shield during a read operation. In both the piggyback and the merged MR heads the shield layers protect the MR sensor from stray magnetic fields, such as fields from adjacent data tracks and processing circuitry, these components being part of a magnetic disk drive.
Unfortunately, both shield layers in a piggyback MR head and the first shield layer in a merged MR head may adversely affect the operation of the write coil. Both the write coil and the one or more shield layers are located in an insulation stack region which is defined by the insulation layers above and below the write coil and which is located between a pole tip region and the back gap. There is a strong inductive coupling between the write coil and the one or more shield layers, which significantly adds to the reluctance of the write coil. When current is conducted through the write coil, flux induced into the one or more shield layers causes a counter flux field which opposes the flux field generated by the write coil. In order for the write coil to create a flux field of acceptable magnitude it must be enlarged to accommodate the effects of the counter flux field. This causes an additional problem. When the one or more shield layers are subjected to a high peak magnitude flux field, magnetic domains in the shield layers may be rotated substantially from an easy axis. When the magnitude of the flux field decreases these domains may not resume to their original orientations. Because of magnetostatic coupling between the shield layers and the MR sensor, the bias point of the MR sensor may change if the shield layer domain disorientation is great enough. A change in the bias point may change the response of the MR sensor to such an extent that the read back signal degrades.
Thus, there is a strongly felt need to reduce the influence of the read head shield layers on the operation of the write head and to reduce the influence of the write head via the shield layers on the operation of the read head.
The prior art structures of piggyback and merged MR heads make their fabrication difficult. In this regard, the height of the insulation stack above the write gap significantly increases the vertical profile of the second pole piece. During fabrication, the high vertical profile on the second pole piece makes it difficult to reduce the aspect ratio (thickness to width) of the second pole tip and to control the smoothness and perpendicularity ("definition") of the second pole tip's sidewalls.
The aspect ratio is determined by the ratio of the height of the photoresist masking layer, required to build the second pole tip, to the width of the second pole tip. In order to write at high data rates the width of the second pole tip must be submicron. Assuming a desired width of the second pole tip is one micron and the height of the photoresist to build the second pole tip is 10 microns, the aspect ratio is 10. As is known, it is very difficult to fabricate a well defined second pole tip with an aspect ratio of 10. Poor definition of the second pole tip sidewalls can result in poor resolution of written data. Thus, there is a strongly felt need to reduce the second pole tip's aspect ratio so that high resolution, high data rate write heads can be fabricated to match the high resolution of the read heads combined therewith.
Another item of concern in piggyback/merged MR head operation is presented by the thinness of the read head insulation layers and the potential for breakdown presented thereby.